The paper deals with the evaluation of shared services for information systems as an approachfor optimizing IS costs. The consolidation of IS processes and re- sources in a shared service centre can be useful if independent IS departments with redundant services exist after a merger, in conglomerates or in other kinds of co-operation. Six case studies are presented in the paper. Thecase studies are characterized bya difference between the management expectations before start of shared ser- vice evaluationand the resultsafter investigation. The reasons for the discrepancies give an input under which circumstances shared service considerations can succeed and when they possibly fail. The outcome leads to corresponding recommendations. The paper touches the change of management position to the question of core business, the synergy pyramid explaining when sufficient cost reduction can be ex- pected, the over-and underestimating of implementa- tion costs and the involvement of staff in the decision process.